Team Fortress 2 Trailer 1 by Valve Software, released via. Steam on July 19th, 2006. Original download page
This trailer shows the 9 classes in a short montage. It interestingly has old models and content which were changed before release - including the uniforms of the Soldier and Engineer, the old Demoman's MIRV (stick) grenade, the scout using a submachine gun instead of scattergun, the silenced pistol instead of a revolver for the spy, and the later-removed Medic syringe.
The map used, 2Fort, also underwent changes before release, adding a bridge over the middle path and other cosmetic differences.
The video also contains no voices, which were likely not recorded by the time.